The invention relates to a deflection yoke for a cathode ray tube, the deflection yoke comprising a set of line deflection coils, a set of field deflection coils surrounding the set of line deflection coils, the set of field deflection coils comprising wire strands and having first void spaces between the wire strands, and a ferrite core surrounding the set of field deflection coils, second void spaces being present between the field deflection coils and the ferrite core.
WO 00/44028 describes a deflection yoke (also called deflection unit) for a cathode ray tube in which the first and/or second void spaces are filled with a magnetic material. Thus, external magnetic stray fields are reduced and the sensitivity of the deflection coils is increased.
The magnetic material may comprise a plastic deformable magnetic material, comprising a resinous material containing a filler of soft-magnetic particles, such as small grains of milled ferrite.
The voids may be filled by injection molding or insertion molding. In the case of injection molding, a material is caused to flow out of a nozzle into the voids after exerting a pressure on a reservoir containing the material. By applying a subsequent heating or drying step, the material is immobilized in the voids. Another filling method is provided by insertion molding. In this case, the object to be filled is surrounded by a dedicated mold, whereafter the voids are filled with the material under a relatively high pressure. Both methods of applying the magnetic material have the drawback that the filling process is dirty and cumbersome.
It is an object of the invention to provide a deflection yoke in which the voids are filled with a magnetic material by means of a clean and simple method. The deflection yoke according to the invention is characterized in that the first and/or second void spaces are filled with a preformed insert comprising magnetic particles. The use of a preformed insert renders it no longer necessary to apply a fluid or paste composite containing ferrite particles and provides a very clean method of applying the magnetic particles.
This aspect as well as other aspects of the invention are defined in the independent claims.
Advantageous embodiments are defined in the dependent claims.
These and other aspects of the invention will be elucidated with reference to the embodiments described hereinafter.